While collapsible structures are not in themselves new, they have been attended by various difficulties, such as multiplicity of parts, which render such devices difficult to erect and difficult to maintain in an erected position with the consequent danger of loss of parts when the device is collapsed. Examples of prior art collapsible structures are shown in U.S. Pat. Nos. 2,405,627; 2,790,978; 1,937,729; 2,346,081; 2,636,196; 3,028,612; and 3,416,170.
The instant invention overcomes this difficulty since the structure disclosed comprises only three main elements; i.e., a flexible skin member having end pieces secured thereto, and two compressible members. Upon removal of the compressible members, the end members and skin can be rolled into a compact bundle. The compressible members have been made separable so that they may be stored in the same bundle. A dinghy employing the herein disclosed principles has been erected and dismantled in less than one minute.
Briefly in accordance with this invention, controlled longitudinal extension is provided in any structure of foldable characteristics by means of a chord compression system or mechanism. In essence, a suitable structure is provided with a pair of rigid or semi-rigid end sections and longitudinal members capable of providing pressure between the two rigid or semi-rigid end members which will hold the structure in erected position. Wires or cables are provided in the flexible intermediate portion of the structure to limit the amount of stress imposed upon the flexible fabric by these compressible members. By removing the longitudinal stressing members the structure can be folded transverse to the longitudinal axis. The means for providing chord compression in each of the longitudinal members is achieved by means of hollow compression tubes which may be either round or square or any suitable shape. At one end of said tubes there is a socket which will fit upon a ball secured to one of the end members. At the opposite end of the tubes is a cut-out or bifurcated device which is adapted to slide along a bar secured to the other end member. The entire longitudinal member or tube, when the male member is in the female member, is longer in physical dimensions than that of the longitudinal dimension of the erected structure such that the bifurcation in the outer end of the tube may be placed diagonally off center and then slid outboard forcing the end members apart and thereby holding them and the skin distended.
In the particular embodiment disclosed herein, a dinghy is shown. In such embodiment a cable is molded or otherwise secured to the gunwale portion of the flexible skin and to each end member and this cable is specifically dimensioned such that when the longitudinal member is in place it prevents overloading of the skin at that particular side of the dinghy in tension; the cable restricting the amount of load taken by the skin. The end members of the device are generally flat as compared to the box construction of my prior U.S. Pat. No. 3,416,170, and constructed either hollow or completely solid. The fore and aft positions of the end members relative to the longitudinal axis of the structure is controlled solely by the accurate pre-cut shape of the flexible fabric affixed to the end pieces. No mechanical relative positioning system such as knife-action and so forth is used. Absolute control of this relationship can be obtained by exacting control of the length of the two flexible cables or wires. The positioning of the longitudinal members where they connect to the end pieces is somewhat critical to maintain the assembled dinghy in its desired position and is preferably slightly below the horizontal centerline of each end member. From the above it can be seen that it is possible to generate or erect a structure, such as a boat, a shelter or a collapsible container with two or more essentially flat planes at their extremities with a minimum of two compression beams. In the case of a boat or dinghy, floatation modules may be mounted upon the longitudinal compression members to provide the required U.S. Coast Guard floatation. These floatation modules may also act as longitudinal ribs maintaining the shape of the fabric when it is subjected to lateral loading and outside pressure.
Dynamic fatigue has been eliminated at the structural joint between the flexible fabric and the end members. The coated fabric of the flexible portion of the structure has been cemented or molded to an intermediate elastomeric extrusion having a laterally extending male member which fits into a complementary shaped female groove disposed within the side and bottom edges of the end members. To maintain the above in assembled position, a tensioned cable extends through an aperture in the male member. By this arrangement all bolts and rivets and so forth have been eliminated from the mounting of the flexible skin to the two end members. The elastomeric extrusion fits tightly in the groove in the end members and the groove is coated with adhesive sealant or bedding compound. The elastomeric extrusion is then pressed into the groove. The internal cable is then tightened along the entire periphery of the end member thus effectively retaining the elastomeric extrusion in the groove with a minimum of reliance upon a bonded joint. This method enables the connection of highly incompatible materials (from an adhesive standpoint) such as plastics of the olefin group and elastomeric materials, particularly with the structural foam plastics showing poor mechanical fastener retention and having low compression value. In none of the modifications do any sharp angles or corners appear between the skin member and the end members. I therefore provide a natural and progressive change of direction of the fabric which by its nature is opposed to the deformation expected from practical load forces and avoids the sharp break that would normally result from a hard angle type of construction. In the case of a dinghy each of the two longitudinal members exert a force of approximately 150 pounds per square inch against the end members. Due to the pivotal action of one end of the structural member and the slide action of the opposite end, a larger mechanical advantage is achieved whereby the actual force to cause erection or collapse of the device by sliding the structural longitudinal member along the bar is extremely small.
The structures employing the principles of the present invention can be used for humam occupation or for the storage and shipment of goods. They can be readily erected and collapsed and can be folded into a small and compact state for ease and convenience or transport and for storage when not in use.
While the present invention is particularly useful and suitable for such purposes as collapsible shelters, containers or vessels for example, the description and illustration of a preferred embodiment of the invention will be directed toward a collapsible boat, particularly of the dinghy type. It is to be emphasized that no restrictions or limitations are intended or are to be placed on the scope or applications of the invention thereby. Rather any limitations or restrictions on the present invention are determined solely from the definition of the invention as recited in the appended claims.